Foil transport arrangement in hot process embossing printing machines

ABSTRACT

A foil transport arrangement in hot process embossing printing machines which provides intermittently acting forward pulls of the foil ribbon in different lengths and in a predetermined sequence. The various forward pulls are formed of several sequentially occurring normal forward pulls of a given length with a concluding longer forward pull. The invention permits the use of a large number of control steps by a plurality of oscillating elements which operate either singly or in combination, subject to automatic control by electrical impulses. The flexibility and control is largely obtained through the use of directional or free-wheeling couplings between a driven shaft and the forward pull assembly.

United States Patent Wetzel et al.

[451 Dec. '18, 1973 FOIL TRANSPORT ARR ANGEMENT IN HOT PROCESS EMBOSSING PRINTING MACHINES [75] Inventors: Roland Wetzel, Ziegelhausen; Hugo Rambausek, Wiesloch, both of Germany [73] Assignee: Heidelberger Druckmaschinen Aktiengesellschaft, Heidelberg, Germany [22] Filed: Nov. 23, 1971 211 Appl. No.: 201,435

[30] Foreign Application Priority Data Nov. 25. 1970 Germany P 20 58 058.9

[52] US. Cl. 226/123, 226/157 1511 Int. Cl. B65h 17/26 [58] Field of Search .i 226/157, 123

[56] References Cited UNITED STATES PATENTS I73Z7U4 10/1929 Wcgncr 226/123 3,276,650 10/1966 Larkin 226/123 Primary Examiner--Allen Ni Knowles Attorney-Arthur E. Wilfond et a].

[57] ABSTRACT A foil transport arrangement in hot process embossing printing machines which provides intermittently acting forward pulls of the foil ribbon in differentlengths and in a predetermined sequence. The various forward pulls are formed of several sequentially occurring normal forward pulls of a given length with a concluding longer forward pull. The invention permits the use of a large number of control steps by a plurality of oscillating elements which operate either singly or in combination, subject to automatic control by electrical impulses. The flexibility and control is largely obtained through the use of directional or free-wheeling couplings between a driven shaft and the forward pull assembly.

6 Claims, 9 Drawing Figures UPPER DEAD L" CENTER LOWER ,DEAD CENTER EMENIED DEC] 8 i975 3,779 442 SHEET 10F 4 UPPER DEAD CENTER LOWER DEAD CENTER SHEET 2 (IF 4 PATENIEU nu: 18 I975 FIG. 3

FIG. 4

SHEET 3 BF 4 PATENTEU DEC 18 I975 FIG. 5

Fl G. 6

ssLgg /m SHEET Q 0F 4 PATENIEDMC 1 8 1915 a LOWER DEAD CENTER FOIL TRANSPORT ARRANGEMENT IN HOT PROCESS EMBOSSIZNG PRINTING MACHINES The invention relates to a foil transport arrangement and particularly for use with hot process embossing printing presses, which provides intermittently acting forward pulls of the foil ribbon in different lengths and in a predetermined sequence.

Foil embossing machines are known which utilize a single forward pull of predetermined length which may be continuously adjusted within wide limits and sequentially acts on the same foil ribbon. The pull on the ribbon here takes place in a known manner by means of a-friction contact between a so-called forward pull roller and a pressure roller, the forward pull roller being the driving element. Ordinarily, a rocker. arm serves to provide the intermittent movement which is translated to the forward pull roller byway of a chain, a chain wheel and a forward pull shaft. In order to maintain the forward pull roller at rest during the return phase of the rocker, there is provided a directional coupling; for instance a free wheel coupling, which acts to provide a driving connection in the direction of the transport and to disconnect the driving connection during the rocker return stroke.

This type of drive, especially when several sequentially arranged embossing dies are used and due to the difference of the embossing designs, permits only a very poor utilization of the foils during an operating run. A relatively large portion of foil remains unused. In order to attain an improved utilization of the foil, frequently, the expedient is resorted to which permits the already utilized foil to be run through the foil embossing press two or more times. The degree of utilization of the foil will of course be improved thereby, but will, however, increase the expectation of not inconsiderable difficulties in servicing and time expenditure. A further possibility exists to improve the utilization of the'foil, which'c'alls for a decrease inthe number of thesequentially arranged embossing dies and instead provides for an increased number of machine runs.

It has been" found that the foil will be subject to an improved utilization during a single run only when several forward pulls having different lengths are being used in a'continuously repeated cycle. These cycles, for instance, may be formed of several sequentially occurring normal'or short forward pulls" of equal length with a concluding longer forward pull (median forward pull"). It may also be useful to introduce a further, still longer forward pull. In this case, the longest forward pull concludes the entire cycle which consists of several short cycles (composed respectively of one or more" short forward pulls and a median forward pull), and. an at-rest cycle. This entire cycle is also repeated continuously.

It is an objectof the invention to provide a simple and inexpensive foil transport arrangement which includes a device for controlling the desired cycling, permitting the use of a large number of control steps as well as the sequential arrangement of forward pulls of different lengths, as, for instance, required for foil embossing machines.

In accordance with the invention, the object is achieved inthat the chain drive, known as such, is enlarged beyond the driving rocker arm furnishing the standard forward pull, by the addition of one or more rocker arms which are coupled to the driving rocker in accordance with a predetermined program.-These added rockers are designed to provide the longer forward pulls and to render inoperative the continuously occurring standard forward pull by an overriding arrangement. The chain wheel which drives the forward pull shaft forming a rigid unit with the forward pull rol-' ler for the standard forward pull over a directional coupling (free-wheeling) whenever the forward pull shaft is to remain behind the chain wheel while the driving connnection is automatically inactivated when the forward pull shaft runs ahead. This lead is produced by the rocker arms which have been added as required and which produce the larger forward pull. The insertion of the added rockers is preferably controlled by means .of a control device furnishing the required program. The control device may consist, for instance, of one or more "counters of known construction such as impulse or sheet counters, whose counting is synchronized with the forward pulls of the transport arrangement and the last counting step of which causes an impulse within 'a given counting range, which controls the activation or inactivation of one or more added rockers and which thereby causes a different forward pull. The counters,

' known as such, thus act on the one hand in accordance with their original function, namely as counters in that they count the forward pulls. On the other hand and primarily, they function as programmed control devices.

While it is sufficient to provide a single impulse or sheet counter for foil transport arrangements with two forward pulls, in accordance with a further embodiment of the invention, two counter devices are coupled with one another, when three forward pulls are used, such, that their counts are synchronized and the last count of the second counting device changes the transport arrangement over to a third forward pull with the largest length.

Other featurestwhich are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as foil transport arrangement in hot process embossing printing presses, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The invention, however, together with additional objects and advantages thereof, will be best. understood from the following description when read in connection with the accompanying drawings, in which:

FlG. l shows a foil transport arrangement having two forward pulls showing two rockers coupled to one another;

MG. 2 shows a detail of FIG. 1',

FIG. 3 is the transport arrangement inaccordance with FIG. 1, in a side view;

FIG. 4 shows a schematic arrangement of animpulse counter for the control of two forward pulls;

FIG. 5 shows the impulse counter of FIG. 4 in a schematic form; I

FIG. 6 is a schematic view of two impulse counters for the control of three forward pulls;

FIG. 7 is the schematic view of the two impulse counters of FIG. 6;

FIG. 8 shows in a perspective view a foil transport arrangement-for two forward pulls with a driving rocker and an electromagnetic ,coupling to the forward pull shaft; and

FIG. 9 shows the forward pull shaft in accordance with FIG. 8 with a driving means for coupling thereto.

FIGS. 1 to 3 show a foil transport arrangement for two forward pulls, wherein a forward pull rocker unit, controlled by an adjustable counting unit, furnishes the foil transport. Foil 3 is transported by means of friction contact between a driven forward-pull roller 1 and a spring-loaded pressure roller 2. The movement of the forward pull shaft 4, rigidly connected with a forward pull roller 1, is caused by chain wheels 5 and 6, which respectively act on the forward pull shaft 4 through freewheel units 7 and 8. Chain 9 together with chain holder 10 connects chain wheel 5 with rocker 11, the latter forming a portion of a rocker crank shaft gear together with coupling 12. The driving crank has not been shown.

The second rocker 13 is supported through a roller bearing independently of rocker 11 on the hub thereof; a chain holder 14 forms a connection with the chain wheel 6 by way of the chain 15. The latch 16 is disposed on rocker 11 so as to engage a counter latch 17 arranged on rocker 13. The pawl or latch 16 is controlled by means of a plunger 18 which is driven in opposition to spring 20 by meansof an electro-magnet 19.

The chains are under continuous pulling tension which is provided by springs 21 and 22. The rocker arm 13 is maintained in a disconnected condition against stop 24 in upper dead center position by means of a spring 23 (chain holder 14 is in 0 position) or by means of the pull from chain 15. A friction brake 25 acts to brake the forward pull roller 1 (FIG. 3).

The operation takes place in such a manner that the adjustment for the desired forward pull length I takes place by way of the chain holder 10 which is radially adjusted in a guiding slot on the rocker 11. Similarly, the chainholder 14 may be adjusted on rocker 13 for the forward pull length II.

The short forward pull I is attained in that the rocker 11 sets in motion the forward pull roller by way of chain wheel 5. The plunger 18 is thus attracted by means of magnet 19 and maintains the pawl 16 in a disengaged position (FIG.-2), whereby the actuation of the counter pawl 17 is avoided.

Should it be desired to utilize the longer forward pull II, the position of the plunger 18 is adjusted during the return stroke of rocker II (FIG. 1). The approaching pawl does not act to lift out, but is free to engage the counter pawl 17 and after its return to effect the engagement of rocker 13.

Both rockers now move together, whereby the chain wheel 6, which is driven by rocker 13, overrides the chain wheel 5, due to the adjustment for the longer forward pull and thus provides forward pull II. Should it be desired to again provide the short forward pull, the magnet will be made to attract the plunger 18 during the return stroke of the rockers. The approaching pawl contacts the plunger shortly before it reaches the upper dead center position and maintains pawls 16 and 17 from the engaging position. Thus, rocker 13 falls back the short remaining distance to its initial position against stop 24, where it remains at rest. Rocker 11 then moves further by itself until again an adjustment for the longer forward pull II is made.

Compared to forward pull II, the short forward pull l ordinarily is many times smaller. It is therefore possible to choose a chain wheel of a larger diameter for forward pull I, whereby an improved chain run-off is obtained.

A slip brake 25 stops-the forward pull roller 1 after the reversal of the movement of the respective driving chain wheel and prevents further undesired forward pull movements during the return stroke.

The system is capable of further modification by means of the use of additional loose rocker arms.

A magnet 19, used for controlling the pawl coupling 16, according to FIG. 1, receives its controlling impulses from a control arrangement.

The impulse counter 26, which has been shown respectively in front and side views in FIG. 4, may be used for controlling, for instance, a foil transport arrangement as shown in FIGS. 1, 8 and 9, and which may be adjusted respectively to two different length forward pulls. The impulse counter 26 may be disposed at any convenient portion of a foil embossing machine. An electrical connection is provided between an impulse counter and the foil transport arrangement. The service portion of the impulse counter 26 provides a blocking contact 27, an adjustment contact 28 and a scale 29. By .means of the blocking contact 27, the adjustable counting device may be rendered inoperative and may be adjusted by means of the adjusting contact 28. The adjustment may be read on the scale 29. After conclusion of the adjustment step, the former position of the blocking contact 27 is restored in order to fix the set count number.

The operation of a foil embossing machine, which is provided with an impulse counter according to FIG. 4, is such that a forward pull is obtained for each imprint. An impulse generator, which has not been illustrated, will thereby, for a single cycle operation during each machine rotation, be struck by a rotating or oscillating machine element and generates an electrical control impulse 30 (FIG. 5), which effects the subtraction in the counter by respectively one number for each imprint from a predetermined starting value. In the embodiment shown, the attainment of the count zero in the impulse counter activates an electrical contact 31, which, by means of a control element forming part of the foil transport arrangement, e.g. the electro-magnet 19 in FIG. 1, initiates a longer than the normal forward pull. Subsequently, the counting device automatically returns by way of the control switch 37 to the preselected counting number and repeats the same cycle. Thus, the foil transport arrangement carries out, in accordance with the number prescribed for the impulse counter, either normal or short forward pulls, while a longer forward pull is furnished for each attainment of the count zero.

Some complicated embossing designs require three different length forwardpulls in order to obtain the best possible utilization of the foils. Accordingly, if a foil embossing machine is provided with a foil transport mechanism which is adjustable for three different forward pulls, two impulse counters must be provided.

FIG. 6 shows the arrangement of two such impulse counters 33 and 34, which are quite identical in their construction. While impulse counter 33 may be adjusted for a number of normal or short forward pulls, followed by a medium length forward pull, impulse counter 34 may be adjusted for the total number of the desired short and median forward pulls. This impulse counter thus provides an impulse which terminates the entire cycle with the longest forward pull; the impulse will be extin guished through the impulse controllingv the longest forward pull. Both counters 33 and 34 are again provided with a blocking contact 27, an adjustment contact 28 and the indicator scale 29. The operation of the double counter mechanism, as shown in FIG. 6, is as follows:

After depressing of the blocking contact 27 of the impulse counter 33, the counting arrangement may be adjusted by means of actuation of one or more adjustment contacts 28. The blocking key 27 is again released and the adjustment set thereby, as soon as the desired number appears on the indicator scale 29 corresponding to the prefigured number. of the normal forward pulls for a short cycle. Thereupon, the blocking key 27 of the impulse counter 34 is actuated so as to render its counting mechanism adjustable. By depressing the adjusting key 28, the total number of the forward pulls occurring within the entire cycle is fed into the impulse counter 34, except for the longest forward pull. The blocking key 27 is now released. The operation of this double counter corresponds essentially to that described in connection with FIGS. 4 and 5. Here, too, the foil embossing machine requires a forward pull for each impression and thereby providesfor a single operating run after each embossing machine rotation (in the printing position) a control impulse 30 for both counting de-' vices-33 and 34 (FIG. 7).

In response to the incoming impulse, counter 33 as well as counter 34 each, respectively, subtract a single number. As counter 33 attains the zero position, an electrical contact 35 is released. I

The electrical contact 35, upon release, renders the adjustable foil transport arrangement to a control action through electromagnet 36, involving a forward pull length change, to a middle forward pull. Thereupon, the counter device returns to its initial position'through an automatic'restoring switch 37. The short cycle then begins all over again.

As already mentioned hereinabove, the impulse 30, derived from the machine, every time releases a control action of the impulse counter 34, which steadily approaches the zero count during the continuous repetition of the shortcycle. As the zero position is attained, an impulse 38 is produced, which initiates the longest forward pull through electromagnet 39, not further il-. lustrated, and at the same time prevents the actuation of magnet 36 through relay 4t and contact 42. It is in this connection of no consequence whether the next to the last step of the entire cycle has been a short or middle forward pull. Thereafter, the impulse counter 34 is automatically restored to its initial position over switch 40 and, at the same time, the counter 33 is also restored through switch 37, controlled by relay 41, and the entire cycle begins anew.

The invention is not limited to the control system as shown. It is also possible, as already mentioned above, to replace the impulse counters through mechanically actuated counters. Similarly, beside electrical, also electronic counters are possible. Counters do not necessarily act to subtract but may also act as adders; it is also possible to combine different types of counters. It is also possible to use counters in connection with other apparatus.

The magnet 19, as shown in FIG. 1,for the purpose -of controlling-the paw] coupling 16, receives its control impulses from acounter shown in FIGS. 4 and 5. It is also possible to avoid the electromagnet l9 altogether and to realize the control of the pawl 16 entirely mechanically without any electrical components. Instead of coupling the rockers through pawls, other types of couplings, alone or with the aid of override or freewheel devices, may be used.

Finally, a form of construction may be mentioned, which uses spring traction not for the return of the chain wheels but for the foil transport.

While in the embodiments so far described for realizing different-forward pulls, driven and non-driven rockers have been coupled to one another, an exemplified embodiment will now be described in connection with FIGS. 8 and 9 for two forward pulls wherein the adjustment to the respective forward pull is obtained through a control action on the forward pull shaft system.

The forward pull shaft unit is characterized by a driving rocker which is common to all forward pulls. Forward pull I acts through an override, and forward pull II over an override and a coupling on the forward pull roller ll. The apparatus is again constructed in a known manner, such that foil 3 is transported between a forward pull roller l and a pressure roller 2 (FIG. 8). Chain wheels 5 and 6 drive, through a special system (FIG. 9), forward pull shaft 4 together with the forward pull roller 1. Chains 9 and 15 are on the one side linked over the chain holders l0 and 114 to the rocker ll driven through the coupling 12, on the other to the springs 21 and 22 required for their return movement. The slip brake 25 is provided in order to prevent undesired movement of the forward pull roller.

The construction of the forward pull shaft unit is illustrated in FIG. 9. Two flange bushings 44 and 45, fastened to the side wall'43 of the forward pull apparatus, serve as a bearing on the one side, directly, and on the other by way of the chain 'wheel of the forward pull roller linked to the forward pull shaft ll. Chain. wheel 5 drives the forward pull roller 4 over a free wheel mechanism 7. Chain wheel 6, journalled in the bushing 45, is connected with'guide ring 49 over free wheel device 46, the housing 47, and the cam 49, The anchor disc 50 is wedged on the shaft 4 over an adjusting spring 51. The supply of energy to the coupling is provided with out a slip ring; the impact stop 52 determines the position of the magnet body 53.

The operation takes place in such a manner that the forward pull I is applied to the forward pull shaft 4 over chain wheel 5 and free wheel device 7, while chain wheel 6, together with rocker 1111, released from the shaft 4 by the opened coupling 49/50 moves freely and without affecting the forward pull. Should the longer forward pull ll be desired, coupling 49/50 will be locked in at a desired moment during the return stroke of the rocker through an impulse obtained from the counting device. Chain wheel 6, which is also in motion, rotates unhindered to the upper dead center position due to the rearwardly open coaster-device 47 in spite of elements 47 and 43, which are connected to the forward pull shaft4 and are therefore at rest. During the following transport stroke, coaster 46 is closed and chain wheel 5 and coaster 7 are overridden. At the conclusion of forward pull II chain wheel 6, in spite of the locked-in coupling 49/50, may return unhindered to the initial position at the upper dead center. The release of the coupling 49 and 50 may take place during a desired portion of the returnstroke. Aifter the decoupling, one or more forward pulls I may occur again.

Since the short forward pull ordinarily is many times smaller than the longer forward pull, it is possible to select for the forward pull l a chain wheel having a larger diameter whereby a better chain run off may be obtained.

in the arrangement of the construction as described, only the small mass of the parts 47/48 is reduced to the zero velocity of the forward pull shaft, which is at rest at this time. This small energy permits extraordinarily short engagement operations with very small coupling dimensions. It is also possible to arbitrarily select the control timing for the coupling during the return stroke, so as to obtain a large safety interval from the time of the motion reversal. The system may also be enlarged to provide more than two forward pulls. The additional chain wheels necessary therefor here, too, are connected over a free-wheel device and a coupling to the forward pull shaft 4, respectively.

The control of the electromagnetic coupling in systems having two forward pulls may be carried out, for instance, by means of one counter, according to FIGS. 4 and 5, and those having three forward pulls including two electromagnetic couplings by means of two counters combined, according to FIGS. 6 and 7. Construc tions are also possible in which the free-wheel arrangement between coupling and chain wheel 6 may be avoided.

There are also solutions, wherein the forward pull 1, as described, is translated onto the forward pull shaft 4 over chain wheel and free wheel device 7-, while the chain wheels necessary for additional forward pulls are respectively connected with chain wheel 5 by way of a free wheel device and a coupling, or only by way of a single coupling.

It is claimed:

1. Foil transport arrangement in embossing machines comprising means for imparting forward movement to a foil along'the main longitudinal dimension thereof having the character of an operation cycle, said forward movement imparting means comprising a driven shaft and a pair of rollers on said shaft for receiving the foil therebetween; means for translating said movement into at least one intermittent forward pull for a given operating cycle, said translating means comprising at least one driven oscillatory element, means for directionally coupling said element to said shaft, and means for intermittently controlling the operativeness of said coupling; means for varying the length of said forward pull, said forward pull varying means including adjustable driving means connecting said oscillating element and said coupling, means for providing additional forward pulls and for controlling the length of individual forward pulls, means for effecting a sequential order of said one and said additional forward pulls, at least one electro-mechanical counter device for providing electrical control impulses for application to said directional coupling element for.contr0l thereof, and means for synchronizing said counter device with said intermittent forward pull translating means.

2. The arrangement according to claim 1, wherein said counter device includes means forv presetting a counting range whereby a control pulse is providable at a predetermined point of the operating cycle and further including at least a second oscillating element, means for linking said one and second oscillating elements and means actuatable by said counter device for controlling said linking means, whereby the two elements may be connected and disconnected for common and individual movement, a forward pull of one length being substituted for a pull of another length thereby.

3. Arrangement according to claim 2, further including a second counting device, means for synchronizing the counting steps of said devices, and means in said second counting device to provide a control impulse, and means for providing a third intermittent forward pull controlled by said last named control impulse.

4. Foil transport device for imparting forward movement to a foil along the main longitudinal dimension thereof, comprising a first rocker mounted for oscillation about an axis, a second rocker mounted for oscillation about the same axis, a first holder slidably mounted on said first rocker, a second holder slidably mounted on said second rocker, drive means having a roller which engages said foil to impart said forward movement to said foil, first and second operative means operatively connected between said first holder and said drive means and between said second holder and said drive means respectively whereby oscillating movement of said first and second rockers are operable to import forward movement to said foil, and means selectively operable to connect said two rocker arms together to provide simultaneous oscillation and to disconnect said two rocker arms so that only one of said rocker arm oscillates.

5. Foil transport device according to claim 4 wherein said drive means includes a shaft on which said roller is mounted, sprockets mounted on said shaft, and a pair of chain means each having one end thereof connected respectively to said first holder and to said second holder, said chain means being biasingly held in engagement with said sprockets.

6. Foil transport device according to claim 4 wherein said selectively operable means includes a latching member pivotally mounted on one of said rocker arms and pivotal to engage and disengage a latch on the other rocker, and means for pivoting said latching member between a latch engaging position and a latch disengaging positions. 

1. Foil transport arrangement in embossing machines comprising means for imparting forward movement to a foil along the main longitudinal dimension thereof having the character of an operation cycle, said forward movement imparting means comprising a driven shaft and a pair of rollers on said shaft for receiving the foil thErebetween; means for translating said movement into at least one intermittent forward pull for a given operating cycle, said translating means comprising at least one driven oscillatory element, means for directionally coupling said element to said shaft, and means for intermittently controlling the operativeness of said coupling; means for varying the length of said forward pull, said forward pull varying means including adjustable driving means connecting said oscillating element and said coupling, means for providing additional forward pulls and for controlling the length of individual forward pulls, means for effecting a sequential order of said one and said additional forward pulls, at least one electro-mechanical counter device for providing electrical control impulses for application to said directional coupling element for control thereof, and means for synchronizing said counter device with said intermittent forward pull translating means.
 2. The arrangement according to claim 1, wherein said counter device includes means for presetting a counting range whereby a control pulse is providable at a predetermined point of the operating cycle and further including at least a second oscillating element, means for linking said one and second oscillating elements and means actuatable by said counter device for controlling said linking means, whereby the two elements may be connected and disconnected for common and individual movement, a forward pull of one length being substituted for a pull of another length thereby.
 3. Arrangement according to claim 2, further including a second counting device, means for synchronizing the counting steps of said devices, and means in said second counting device to provide a control impulse, and means for providing a third intermittent forward pull controlled by said last named control impulse.
 4. Foil transport device for imparting forward movement to a foil along the main longitudinal dimension thereof, comprising a first rocker mounted for oscillation about an axis, a second rocker mounted for oscillation about the same axis, a first holder slidably mounted on said first rocker, a second holder slidably mounted on said second rocker, drive means having a roller which engages said foil to impart said forward movement to said foil, first and second operative means operatively connected between said first holder and said drive means and between said second holder and said drive means respectively whereby oscillating movement of said first and second rockers are operable to import forward movement to said foil, and means selectively operable to connect said two rocker arms together to provide simultaneous oscillation and to disconnect said two rocker arms so that only one of said rocker arm oscillates.
 5. Foil transport device according to claim 4 wherein said drive means includes a shaft on which said roller is mounted, sprockets mounted on said shaft, and a pair of chain means each having one end thereof connected respectively to said first holder and to said second holder, said chain means being biasingly held in engagement with said sprockets.
 6. Foil transport device according to claim 4 wherein said selectively operable means includes a latching member pivotally mounted on one of said rocker arms and pivotal to engage and disengage a latch on the other rocker, and means for pivoting said latching member between a latch engaging position and a latch disengaging positions. 